Angular Reference Problem for Three-Phase Distribution System State Estimation

State Estimator is a key monitoring feature for the conception of Smart Grids. Although largely used in transmission systems, the implementation of estimators that correctly capture the Distribution Systems' (DSs) behavior is challenging, partially due to these circuits' asymmetric and unbalanced nature. As a result, a three-phase representation of the network is required. Despite some good theoretical results with this formulation, they usually use a phase angle reference for each phase, assuming balanced voltage phase angles at the Reference Bus (RB), which does not enable the estimator to encompass the unbalanced nature of those circuits. This article investigates the number of reference angles required for a three-phase Distribution System State Estimator (DSSE) from an observability point of view. Based on this concept, this study derives a condition for the use of only one phase angle as the reference. The article also introduces a method that properly represents the RB and promotes the use of one reference in most cases. Results from IEEE 34, IEEE 123, and 1058 bus Brazilian test feeders show the approach's feasibility and the negative effect of the mistreatment of the RB.